def build_person(first_name,last_name):
    person = {'first':first_name,'last':last_name}
    return person

print(build_person("zhangsan","lisi"))

def build_persion1(first_name,last_name,age=None):
    person = build_person(first_name,last_name)
    if age:
        person['age'] = age
    return person

print(build_persion1("zhangs",'lisi',45))